Firstly, disable the built-in graphics card via the BIOS, that will eliminate one layer of confusion. If Ubuntu doesn't find the built-in graphics, there's no need to work around it (and it won't if it's been disabled via the BIOS).
Secondly, follow the instructions here:
https://help.ubuntu.com/community/Video
It's a bit difficult to get the nvidia card running, but if you follow step-by-step, you should be on your way.